JavaScript单元测试与Mocking

npm install --save-dev jest

"scripts": {
  "test": "jest"
}

function processUser(fetchUser, userId) {
  const user = fetchUser(userId);
  return `Processed: ${user.name}`;
}

test('processUser calls fetchUser with correct ID', () => {
  const mockFetch = jest.fn();
  mockFetch.mockReturnValue({ name: 'Alice' });

  processUser(mockFetch, 123);

  expect(mockFetch).toHaveBeenCalledWith(123);
  expect(mockFetch()).toBe({ name: 'Alice' });
});

// api.js
import axios from 'axios';
export async function fetchUserData(id) {
  const res = await axios.get(`/api/users/${id}`);
  return res.data;
}

jest.mock('axios');

test('fetchUserData returns user data', async () => {
  const axios = require('axios');
  axios.get.mockResolvedValue({ data: { id: 1, name: 'Bob' } });

  const result = await fetchUserData(1);

  expect(result.name).toBe('Bob');
  expect(axios.get).toHaveBeenCalledWith('/api/users/1');
});

const mockFs = {
  readFile: jest.fn((path, cb) => {
    if (path === 'valid.json') {
      cb(null, '{"name":"John"}');
    } else {
      cb(new Error('File not found'), null);
    }
  })
};

beforeEach(() => {
  jest.spyOn(console, 'log').mockImplementation();
});

afterEach(() => {
  jest.clearAllMocks();
});